Key Laboratory of Diagnosis and Treatment of Digestive System Tumors of Zhejiang Province, Hwa Mei Hospital, University of Chinese Academy of Sciences, Ningbo, 315010, China.
Ningbo Institute of Life and Health Industry, University of Chinese Academy of Sciences, Ningbo, 315010, China.
Parasit Vectors. 2022 Aug 7;15(1):286. doi: 10.1186/s13071-022-05387-4.
The genus Rickettsia contains the lineages spotted fever group (SFG), typhus group (TG), and transitional group (TRG). The spotted fever group Rickettsia (SFGR) is transmitted by ticks. The tick species Dermacentor nuttalli is considered the main vector carrying SFGR in Inner Mongolia. Studying the genetic diversity and population structure of Rickettsia is essential for developing effective control strategies and predicting evolutionary trends of Rickettsia.
In 2019 we collected 408 D. nuttalli in the Inner Mongolia Autonomous Region, detected the percentage of Rickettsia-positive specimens, and characterized the haplotypes. From the Rickettsia-positive ticks, the gltA and ompA genes were extracted, amplified, and sequenced.
Ten haplotypes of the gltA gene and 22 haplotypes of the ompA gene were obtained. The phylogenetic analysis showed that the haplotypes G1-G7 and G9 of the gltA gene cluster with Rickettsia raoultii, while G8 and G10 cluster with Rickettsia sibirica. Haplotypes O1-O15, O18 and O20-O22 of the ompA gene cluster with R. raoultii, while O16 and O19 cluster with R. sibirica. The average haplotype diversity was 0.3 for gltA and 0.7 for ompA. The average nucleotide diversity was greater than 0.05. Neutrality tests were nonsignificant for Tajima's D results and Fu's Fs results. The fixation index values (F) showed that the degree of genetic differentiation between most sampled populations was small (F < 0.05), whereas some populations showed a medium (F > 0.05) or large (F > 0.15) degree of differentiation. Analysis of molecular variance (AMOVA) revealed that the variation within populations was greater than that between populations. The mismatch analysis of Rickettsia showed double peaks.
We found two Rickettsia spp. (R. raoultii and R. sibirica). The high genetic disparity of Rickettsia allows for easy adaption to different environments. Genetic differentiation between populations is small, and Rickettsia populations do not show a geographically differentiated structure. The high rates of retention and infection of Rickettsia in D. nuttalli together with the animal husbandry exchange in Inner Mongolia gradually led to the harmonization of genetic characteristics of Rickettsia across various regions. Overall, the significant genetic diversity and geographical structure of Rickettsia in D. nuttalli are critical for SFGR control.
立克次氏体属包含斑疹热群（SFG）、斑疹伤寒群（TG）和过渡群（TRG）。斑点热群立克次氏体（SFGR）通过蜱传播。草原革蜱被认为是内蒙古携带 SFGR 的主要媒介。研究立克次氏体的遗传多样性和种群结构对于制定有效的控制策略和预测立克次氏体的进化趋势至关重要。
2019 年，我们在内蒙古自治区采集了 408 只草原革蜱，检测了立克次氏体阳性标本的比例，并对其单倍型进行了特征描述。从立克次氏体阳性蜱中提取 gltA 和 ompA 基因并进行扩增和测序。
获得了 10 个 gltA 基因单倍型和 22 个 ompA 基因单倍型。系统发育分析显示，gltA 基因的单倍型 G1-G7 和 G9 与拉乌尔立克次体聚类，而 G8 和 G10 与西伯利亚立克次体聚类。ompA 基因的单倍型 O1-O15、O18 和 O20-O22 与拉乌尔立克次体聚类，而 O16 和 O19 与西伯利亚立克次体聚类。gltA 的平均单倍型多样性为 0.3，ompA 的平均单倍型多样性为 0.7。平均核苷酸多样性大于 0.05。Tajima's D 结果和 Fu's Fs 结果的中性检验均不显著。固定指数值（F）表明，大多数采样种群之间的遗传分化程度较小（F<0.05），而一些种群表现出中等（F>0.05）或较大（F>0.15）的遗传分化程度。分析分子方差（AMOVA）显示，种群内的变异大于种群间的变异。立克次氏体的错配分析显示出双峰。
我们发现了两种立克次氏体（拉乌尔立克次体和西伯利亚立克次体）。立克次氏体的高遗传差异使其能够轻易适应不同的环境。种群间的遗传分化较小，立克次氏体种群没有表现出地理分化结构。草原革蜱对立克次氏体的高保留率和感染率，以及内蒙古的畜牧业交流，逐渐使各地立克次氏体的遗传特征趋于协调。总的来说，草原革蜱中立克次氏体的显著遗传多样性和地理结构对立克次氏体的控制至关重要。
